Skeletal muscles Flashcards
true or false skeletal muscles act in antagonistic pairs
true
agonist-contracting muscle/antagonist-relaxing muscle
describe the structure of the skeletal muscle (7 features)
- muscle fibres(large bundles of long cells)
- sarcolemma(cell membrane of muscle fibre cells)
- sarcoplasm(cytoplasm of muscle fibre cells)
- T-tubules(inward folds of sarcolemma to spread electrical impulse throughout sarcoplasm)
- sarcoplasmic reticulum(internal membrane network throughout sarcoplasm to store/release Ca2+ ions for contraction)
- mitochondria(provides ATP for contraction)
- myofibril(long cylindrical organelles made of protein specialised for contraction)
muscle fibres are multinucleate, what does this mean?
they contain many nuclei
describe structure of myofibrils
- contains myosin(thick forms dark A band) and actin(thin forms light A band) protein filaments called myofilaments
- sarcomeres(overlapping filament units between Z lines where interaction of filaments causes muscle contraction)
- M-line(middle of sarcomere and myosin)
- H-zone(only myosin)
what is the role of myosin and actin in muscle contraction?
- they both stay the same length so A band (length of myosin) stays same length but they slide over each other=sarcomere contracts
- as a result the following get shorter: sarcomere(Z-line closer to each other)/H-zone(only myosin where it’s not overlapped)/I-band(only actin where it’s not overlapped)
- myosin head binds to actin filaments
Briefly define the sliding filament theory
filaments don’t change length but overlap more,shortening the sarcomere and making the muscles contract
Explain the sliding filament theory
- sarcolemma is depolarised=Ca2+ channels on sarcoplasmic reticulum open.
- Ca2+ diffuses into sarcoplasm then myofibril binding to troponin which causes it to change shape.
- tropomyosin moves being pulled out of active-myosin binding site exposing myosin-binding sites on actin.
- myosin heads bind to myosin-binding site on actin=actin-myosin crossbridges.Ca2+ activates ATP hydrolase in head=ATP hydrolysed to ADP and Pi.
- energy released from ATP hydrolysis causes myosin head to bend pulling actin filament with it in a rowing action.
- New ATP binds to head breaking actin-myosin crossbridge so myosin detaches from actin, head ready to reattach to new binding site to repeat the process.
what is the role of ATP in sliding filament theory?
- move myosin heads which slide actin filaments
- breaks actin-myosin crossbridge
- active transport of Ca2+ in reticulum
- slow process aerobically
how is ATP generated aerobically/anaerobically for muscle contraction?
A-oxidative phosphorylation in mitochondria(needs O2 so good for long low-intensity periods of exercise)
An-glycolysis made rapidly but lactate builds up and causes muscle fatigue so good for short high-intensity periods of exercise
phosphocreatine can also provide energy for muscle contraction,explain how the ATP-Phosphocreatine (PCr) system works
-phosphorylating ADP with phosphate from phosphocreatine=ATP
-PCr stored in cells generates ATP very fast but also runs out after a few seconds
PCr system anaerobic and alactic(no lactate produced)
give features of slow twitch fibres (4 features)
- slow less powerful contractions over a long time period
- good for endurance work or maintaining posture (calf muscle used to stand still)
- uses aerobic respiration but does NOT produce lactate (so not fatigued)
- large O2 store in myoglobin+lots of mitochondria and blood vessels=dark red looking muscles
give features of fast-twitch fibres (4 features)
- fast powerful contractions over a short time period
- good in sprint work and bicep muscles used for weight lifting
- uses anaerobic respiration so becomes fatigued fast(due to lactic acid production)
- less myoglobin,mitochondria and blood vessels=lighter looking muscles
